Method and apparatus for operating gaseous fuel fired heater

ABSTRACT

A method and apparatus for combusting a fuel and air mixture within a combustion chamber, particularly a combustion chamber of a gaseous fuel fired water heater. A pressure relief void is intentionally formed so that a combustion chamber forms communication with a surrounding environment through means other than the exhaust flue and/or a fuel and/or air inlet. During ignition, the pressure relief void allows pre-combustion fluid within the combustion chamber to escape through both the pressure relief void and the exhaust flue. The pressure relief void reduces or eliminates undesirable noise associated with start-up and operation of conventional water heater combustion chambers with premixed burner systems. The pressure relief void of this invention is preferably sized large enough to relieve an ignition pressure pulse from the combustion chamber upon ignition and yet is sized small enough to prevent a combustion flame from passing through the pressure relief void during ignition and/or operational combustion. The water heater may include two burner assemblies, each which can be easily attached or detached, for quick installation and easy maintenance.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a method and apparatus for operating aheater, such as a gaseous fuel fired water heater. This invention alsorelates to a water heater having two or more burner assemblies and amounting apparatus for releasably attaching each burner assembly to abottom wall of a combustion chamber, such as a water heater combustionchamber.

[0003] 2. Description of Related Art

[0004] Many conventional water heater combustion chambers intentionallyoperate with a combustion chamber that is substantially sealed, exceptfor communication with the surrounding environment through a flue stackand an inlet opening for fuel and/or air. In some designs, thecombustion air is introduced into the combustion chamber through arestricted opening, wherein a portion of the air is mixed with fuel inthe burner nozzle and ignited in a primary combustion region and theremaining portion of the air is directed around the burner to completecombustion. The remainder of the combustion chamber is substantiallysealed. U.S. Pat. No. 5,797,355 describes such a gas-fired heater. Thepurpose of the restricted air opening in the combustion chamber is toprevent a combustion flame from passing from the combustion chamber tothe ambient surroundings.

[0005] Alternatively, the heater may be constructed with a substantiallysealed combustion chamber in which all or substantially all of thecombustion air and fuel are directed through an inlet nozzle to theburner, denoted as a fully premixed or simply premixed burner, with theintent of improving burner and overall system performance. For example,U.S. Pat. No. 5,355,841 describes a gas-fired heater with a premixedburner having a substantially sealed combustion chamber. It is apparentthat many conventional designs having premixed burner systems try toachieve a gas tight seal between the combustion chamber and a tank wallin order to limit the entry of secondary combustion air.

[0006] A common phenomenon associated with water heater designsemploying premixed burners is an undesirable noise, upon ignition andduring steady state operation of the combustion chamber. The noise isinitiated by the transient pressure rise associated with burnerignition, and may persist during steady state operation if one or morefrequencies generated by flame instabilities or other periodic energyinput from the burners corresponds with one or more structural orfluidic natural frequencies of the water heater and if there isinsufficient system damping to mitigate the acoustic response. Variousapproaches have been taken to provide noise reduction and/or pressurerelief in the substantially sealed combustion chamber, as taught in U.S.Pat. Nos. 5,317,992, 5,435,716 and 5,791,298, including insulationprovided on the interior of the combustion chamber, a diaphragm on thebottom of the combustion chamber, and openings in the combustion chambercovered by porous material or flaps. These approaches add to system costand manufacturing complexity, and introduce additional components thatcan negatively impact reliability.

SUMMARY OF THE INVENTION

[0007] It is one object of this invention to provide a method andapparatus for operating a water heater wherein a pressure relief void isin communication with the combustion chamber, to relieve chamberpressure during ignition and also to prevent a combustion flame frompassing through the pressure relief void during operational combustion.

[0008] It is another object of this invention to provide a gaseous fuelfired water heater that has two burner assemblies mounted within orexposed to a combustion chamber.

[0009] It is yet another object of this invention to provide a mountingapparatus for releasably attaching a burner assembly to a bottom wall ora base plate of a water heater combustion chamber.

[0010] The method and apparatus of this invention reduce undesirablenoise associated with ignition and with steady state or operationalcombustion. The method and apparatus of this invention enhance designflexibility by providing a relatively broad range of port loading, thefiring rate per square inch of burner material. The method and apparatusof this invention also enhance scale-up capabilities which allows oneparticular burner assembly design to be used in different operationswith various load settings.

[0011] The above and other objects of this invention are accomplishedwith a method wherein a fuel and air mixture, preferably but notnecessarily pre-mixed and containing sufficient air to completelycombust the quantity of fuel, is introduced into a burner and burned orcombusted within a combustion chamber. The fuel and air mixture isignited within the combustion chamber. An exhaust flue formscommunication between the combustion chamber and an ambient environmentwhich surrounds the combustion apparatus. Combustion products dischargethrough the exhaust flue.

[0012] In a pre-combustion condition, the combustion chamber is filledwith or houses a fluid, mostly air or another suitable oxidant. Uponinitial ignition of the fuel and air mixture, a first portion of thepre-combustion fluid passes through a pressure relief void and a secondportion of the pre-combustion fluid passes through the exhaust flue.Conventional water heater apparatuses having premixed burner systems tryto seal the combustion chamber, except for communication with an airsupply and the exhaust flue, which the prior art refers to as asubstantially sealed chamber. According to this invention, the pressurerelief void is intended to form a combustion chamber which is notsubstantially sealed.

[0013] In one embodiment of this invention, the pressure relief void issized large enough to relieve an ignition pressure from the combustionchamber when the fuel and air mixture is initially ignited yet is sizedsmall enough to prevent a combustion flame from passing through thepressure relief void during ignition and/or operational combustion ofthe continuously supplied fuel and air mixture.

[0014] The pressure relief void can have many different sizes, shapes,forms, and locations with the combustion chamber, as long as aneffective area of the pressure relief void adequately relieves theignition pressure and prevents the combustion flame from passing throughthe pressure relief void during ignition and/or operational combustion.For example, the pressure relief void can be formed by a peripheral gapbetween the combustion chamber wall and a vessel wall, such as of awater tank of the water heater. In other embodiments, the pressurerelief void can be incorporated in the mounting structure for the pilotassembly or the bottom wall or side wall of the combustion chamber. Manydifferent structural elements and configurations can be used to maintainor form the pressure relief void.

[0015] In one embodiment of this invention, the water heater apparatushas two or more burner assemblies mounted to a bottom wall of thecombustion chamber. In one embodiment, two burner assemblies arepositioned a distance apart from each other and form a catch areabetween the burner assemblies. The catch area is preferably but notnecessarily located on the bottom wall, for catching debris falloutand/or condensation which may occur during combustion.

[0016] In another embodiment of this invention, each burner assemblypreferably has a mounting apparatus for releasably attaching the burnerassembly with respect to a bottom wall that at least partially definesthe combustion chamber. The mounting apparatus includes a retainer whichis secured, either fixedly or releasably, to the burner assembly. A clipis attached to the bottom wall. The clip has an end portion spaced fromthe bottom wall and thus forms a receiver. A portion of the retainer canbe engaged within the receiver. Once engaged, a removable fastener canbe used to fasten another end of the retainer against the bottom wall.

[0017] In one embodiment, the fastener is a screw. In another embodimentthe fastener includes a catch or latch which can be removably engagedwithin a shoulder of the bottom wall. Any other suitable connectingdevice can be used to quickly attach and detach the burner assembly withrespect to the bottom wall. The mounting apparatus of this inventionsimplifies field installation and/or maintenance of burner assembliesmounted within water heaters.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The technical features of this invention are described in thespecification and the claims, and are better understood in view of thedrawings, wherein:

[0019]FIG. 1 is a schematic sectional view of a lower portion of a waterheater, according to one embodiment of this invention;

[0020]FIG. 2 is a schematic sectional view, taken along line 2-2 asshown in FIG. 1, of the bottom wall having two mounted burnerassemblies;

[0021]FIG. 3 is an exploded perspective view of a burner assembly,according to one embodiment of this invention;

[0022]FIG. 4 is a schematic view of the burner assembly shown in FIG. 3,but in an assembled condition;

[0023]FIG. 5 is a perspective bottom view of a bottom wall having twoburner assemblies, one attached to the bottom wall and another detachedfrom the bottom wall, according to one embodiment of this invention;

[0024]FIG. 6 is a perspective top view of the bottom wall with the twoburner assemblies, according to the embodiment shown in FIG. 5;

[0025]FIG. 7 is a perspective view of a burner assembly mounted at anangle with respect to a bottom wall, according to one embodiment of thisinvention;

[0026]FIG. 8 is a perspective view of a burner assembly, according toanother embodiment of this invention;

[0027]FIG. 9 is a sectional view taken along a longitudinal axis of theburner assembly as shown in FIG. 8;

[0028]FIG. 10 is a sectional view taken in a direction transverse to thelongitudinal axis of the burner assembly as shown in FIG. 7;

[0029]FIG. 11 is a perspective top view of a lower portion of a watertank attached with respect to an upper portion of a combustion chamberwall, to form a peripheral gap, according to one embodiment of thisinvention;

[0030]FIG. 12 is an enlarged perspective top view of a ledge areashowing a peripheral gap, according to the embodiment as shown in FIG.11;

[0031]FIG. 13 is an exploded perspective top view of a lower portion ofa water tank above an upper portion of a combustion chamber wall, withan arrow showing a direction of attachment to form a peripheral gap,according to one embodiment of this invention;

[0032]FIG. 14 is a partial cross-sectional view of a burner assemblymounted with respect to a bottom wall defining a combustion chamber,according to one embodiment of this invention;

[0033]FIG. 15 is a partial cross-sectional view of a burner assemblymounted with respect to a bottom wall which defines a combustionchamber, according to another embodiment of this invention;

[0034]FIG. 16 is a schematic sectional view showing two burnerassemblies mounted within a water heater, according to one embodiment ofthis invention;

[0035]FIG. 17 is a schematic view showing two burner assemblies mountedwithin a water heater, according-to another embodiment of thisinvention; and

[0036]FIG. 18 is a schematic sectional view of a bottom wall having onearcuate or annular mounted burner assembly.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0037] The method and apparatus of this invention, including individualor combined steps and/or elements, can be used to construct new waterheaters or can be used to retrofit existing water heaters, includingtheir designs, operating methods, apparatuses and/or manufacturingmethods. One operting method according to this invention is described inview of FIGS. 1-4.

[0038] The method and apparatus of this invention are particularlysuitable for gaseous fuel fired water heaters, such as those having anatural draft and/or non-condensing operation. For example, the methodand apparatus of this invention can be used with Volume I Storage TypeGas Fired Water Heaters, according to United States standards such ANSIZ21.10.

[0039] The method of this invention is used to combust a fuel and airmixture within a combustion chamber, such as of a gaseous fuel firedwater heater. As shown in FIG. 1, in a conventional manner, water heater20 comprises combustion chamber 35 which is in communication withexhaust flue 60. Also in a conventional manner, exhaust flue 60 is incommunication with ambient environment 21 surrounding water heater 20.

[0040] As shown in FIG. 4, fuel supply 22 and air supply 23 areintroduced into venturi 24. In one embodiment of this invention, thefuel and the air are mixed within venturi 24 so that a pre-mixed fueland air mixture is supplied to burner material 57 of burner assembly 45.It is apparent that the fuel and the air can be pre-mixed and/or can besupplied to burner material 57 through any other nozzle or inlet or inany other suitable manner known to those skilled in the art ofcombustion.

[0041] As used throughout this specification and in the claims, the termfuel is intended to relate to any gaseous fuel used in combustion, suchas natural gas, propane, and other suitable combustible gases, or anysuitable vaporized fuel. Also as used throughout this specification andin the claims, the term air is intended to relate to atmospheric air orany other suitable oxidant used to combust fuel.

[0042] The fuel and air mixture passes through venturi 24 or any othersuitable inlet nozzle and is discharged from a flame holding device,such as burner material 57. A combustion flame is preferably establishedon the surface of burner material 57.

[0043] As shown in FIGS. 1 and 2, pilot 26 is used to ignite the fueland air mixture. In one embodiment, pilot 26 is used only upon initialignition of the fuel and air mixture. In a combustion system having twoburner assemblies 45, pilot 26 or another suitable ignitor can bestrategically positioned to ignite the fuel and air mixture at thesurface of one burner material 57, which can then be used to light thefuel and air mixture at the surface of another burner material 57. Oncea combustion flame is established or sustained, it is possible toextinguish pilot 26 if the combustion flame then ignites thecontinuously flowing fuel and air mixture.

[0044] In a pre-combustion state, for example before ignition,combustion chamber 35 is filled with a fluid. Depending upon conditions,the fluid may include air and/or combustion products which remain withincombustion chamber 35, such as shortly after shut down of water heater20. Many conventional water heaters with premixed burner systems whichoperate with a combustion chamber that is substantially sealed producean undesirable noise upon ignition due to the transient pressure pulsein the combustion chamber. Except for the communication with the fluestack and the inlet nozzle, these conventional water heaters areintentionally designed to achieve an otherwise completely sealedcombustion chamber, for example to prevent additional combustion airfrom entering the combustion chamber.

[0045] Directly contrary to conventional water heater sealed combustionchambers, the method and apparatus of this invention, in addition toforming communication with exhaust flue 60 and venturi 24 or anothersuitable inlet nozzle, intentionally forms communication betweencombustion chamber 35 and ambient environment 21. In one embodiment ofthis invention, pressure relief void 27 forms the intentionalcommunication between combustion chamber 35 and ambient environment 21,such as shown in FIGS. 1 and 11, through peripheral gap 29.

[0046] In one embodiment of this invention, upon ignition of the fueland air mixture within combustion chamber 35, a first portion of thepre-combustion fluid is discharged through pressure relief void 27 and asecond portion of the pre-combustion fluid is discharged through exhaustflue 60. Pressure relief void 27 is preferably sized large enough torelieve an ignition pressure from combustion chamber 35 upon ignition ofthe fuel and air mixture and yet is sized small enough to prevent acombustion flame from passing through pressure relief void 27 duringoperational combustion of the continuously flowing fuel and air mixture.

[0047] An effective area of pressure relief void 27 can be sized and/orshaped relative to an effective area of exhaust flue 60, so that a firstpressure drop or flow rate across pressure relief void 27 is less thanor significantly less than a second pressure drop or flow rate acrossexhaust flue 60. With such design, the ignition pressure is adequatelyrelieved through pressure relief void 27. The pressure relief uponignition significantly reduces undesirable noise associated with otherconventional water heater sealed combustion chamber designs.

[0048] In one embodiment according to this invention, the effective areaof pressure relief void 27 can be sized as a ratio of the effective areaof exhaust flue 60. The areas can be changed, particularly relative toeach other, to achieve different ratios that vary depending upongeometric and operational parameters of water heater 20. As an example,water heater 20 may have pressure relief void 27 formed by a 0.060 inchgap about a 16 inches diameter combustion chamber 35, which operates incommunication with a 4 inches diameter exhaust flue 60. In thisparticular example, the dimensions result in a ratio of about 0.24 ofthe area of pressure relief void 27 over the area of exhaust flue 60.However, it is apparent that other suitable area ratios can varysignificantly, depending upon the operating conditions and the geometryof water heater 20.

[0049] During operational combustion, such as the condition where thefuel and air mixture continuously flows through burner assembly 45 and acombustion flame is established on the surface of burner material 57,relatively little or no combustion products flow out of the combustionchamber through pressure relief void 27, and relatively little or no airflows into the combustion chamber through pressure relief void 27. Ifdesired, it is possible to control a leakage rate of combustion productsand/or air passing through pressure relief void 27 during operationalcombustion, such as by selecting a different effective area for pressurerelief void 27.

[0050] As shown in FIG. 1, peripheral gap 29 forms pressure relief void27. Peripheral gap 29 is preferably but not necessarily in a range fromabout 0.055 inch to about 0.065 inch, preferably about 0.060 inch.

[0051] Spacer element 30 can be used to maintain peripheral gap 29, asshown in FIG. 1 between chamber wall 25 and vessel wall 40. FIG. 11shows another embodiment of this invention where protuberance 32 extendsfrom chamber wall 25 that partially defines combustion chamber 35, butprotuberance 32 can also extend from the inner surface of the lower edgeof vessel wall 40. Protuberance 32 or another suitable spacer element 30can be positioned at selected circumferential intervals about theperiphery of combustion chamber 35. For example, as shown in FIG. 13,protuberances 32 can be positioned at eight locations, each about 45degrees apart, about the periphery of combustion chamber 35. It isapparent that any other suitable mechanical spacer element 30 can beused to fix a size and/or shape of pressure relief void 27.

[0052] In one embodiment according to this invention, burner material 57is a self-supporting mat structure. The self-supporting mat structuremay comprise a plurality of ceramic fibers coated with a siliconecarbide material or another suitable material. The ceramic fibers can besolidly welded together or otherwise fused into a rigid, porous matrix.The self-supporting mat structure can be processed, for example assheets having a thickness of approximately 0.10-0.15 inch. The porosityof the bulk material may allow a quantity of the fuel-air mixture toflow through the entire surface area. Perforations throughout the bulkmaterial can be formed in a regular pattern to increase or obtain thesuitable port loading, as defined by firing rate per square inch ofburner surface. A suitable burner mat is offered by Schott Gas Systems,and is marketed as a Ceramat® burner mat, which has relatively lowthermal conductivity, a rigid self-supporting structure, and low thermalexpansion, all of which provide a burner with stable combustion, lowemissions, even radiation, fast reaction and a wide modulation range. Aself-supporting mat structure or another suitable burner material 57 canbe mounted with respect to bottom wall 36, such as shown in FIGS. 14 and15.

[0053]FIGS. 7 and 8 show different embodiments for mounting burnermaterial 57 in burner assembly 45. FIGS. 9 and 10 show plenum 53. In oneembodiment, the fuel and air mixture are discharged from venturi 24 oranother suitable inlet nozzle, into plenum 53. The fuel and air mixtureis then discharged from plenum 53 through burner material 57.

[0054] Burner material 57 may be mounted to plenum 53 in burner assembly45 using retainer 47. Insulator 61 can be positioned between bottom wall36 and burner material 57, for example to reduce heat transfer betweenburner material 57 and both bottom wall 36 and retainer 47, and toprevent combustion flames from burner material 57 from quenching orattaching to edges of bottom wall 36.

[0055]FIGS. 5 and 6 show one embodiment of water heater 20 having twoburner assemblies 45 mounted to bottom wall 36. FIG. 5 shows one burnerassembly 45 attached to bottom wall 36 and another burner assembly 45detached from bottom wall 36.

[0056] In one embodiment of this invention, a mounting apparatus can beused to releasably attach burner assembly 45 with respect to bottom wall36. The mounting apparatus comprises flange 64, also shown in FIGS. 3,5, 14 and 15 formed along the edge of plenum 53 in burner assembly 45,such as shown in FIG. 4. Clip 50 is attached to bottom wall 36. It isapparent that clip 50 can be welded, adhered, secured or otherwisemechanically connected to or with respect to bottom wall 36. In oneembodiment, as shown in FIG. 5, clip 50 comprises base portion 52 andend portion 51 which is offset from or with respect to base portion 52.A transition between base portion 52 and end portion 51 forms ashoulder. FIGS. 14 and 15 show another embodiment of clip 50 attachedwith respect to bottom wall 36. In a mounted position of burner assembly45 with respect to bottom wall 36, flange 64 limits movement of burnerassembly 45 with respect to bottom wall 36, such as in a directiongenerally parallel to a longitudinal axis of burner assembly 45.

[0057] In one embodiment, clip 50 comprises slot 49, as shown in FIG. 5.In a mounted position of burner assembly 45 with respect to bottom wall36, seam 46 or another suitable structure of burner assembly 45 isengaged within slot 49, for example to limit movement of burner assembly45 in at least one direction with respect to bottom wall 36, such as ina direction which is generally transverse to the longitudinal axis ofburner assembly 45.

[0058] A removable fastener is used to secure, attach or otherwisefasten an opposite end of flange 64 to or with respect to bottom wall36. Fastener 55 may be a screw, as shown in FIGS. 5 and 14, or a catchor latch 62 as shown in FIG. 15. The catch or latch 62 may attach withina shoulder area of bottom wall 36. As shown in FIG. 15, latch 62 canpivot with respect to bottom wall 36 about pivot 63, which can be a pin,a rod or any other suitable mechanical pivot device. The shoulder areacan be formed by a void within bottom wall 36, a shoulder formed as anintegral part of bottom wall 36 or a shoulder structure attached tobottom wall 36. It is apparent that any other suitable removablefastener can be used in lieu of either the screw or the catch or latch62.

[0059] Flange 64, clip 50 and fastener 55 and/or latch 62 can be used toquickly attach or detach burner assembly 45 with respect to bottom wall36. This is particularly important when servicing a water heater. Thedesign of this invention provides easy access for field installationand/or maintenance.

[0060] In an embodiment where two or more burner assemblies 45 aremounted within combustion chamber 35, each burner assembly 45 ispreferably positioned at a distance apart from each other to form catcharea 38, such as shown in FIGS. 2, 6, 16 and 17. In another embodimentwhere only one burner assembly 45 is mounted within combustion chamber35, burner assembly 45 forms an annular shaped burner that also formscatch area 38, such as shown in FIG. 18. According to such embodiment,the annular shape can be replaced with a simple arcuate shape which doesnot necessarily form a complete circle. In either embodiment, catch area38 can be used to gather or collect debris fallout, condensation or anyother combustion product resulting from operation of water heater 20.Catch area 38 is preferably centrally located on bottom wall 36 but maybe located in any other suitable position, depending upon the overalldesign and structure of water heater 20.

[0061]FIGS. 16 and 17 show general arrangements of water heater 20, withtwo burner assemblies 45 mounted at an angle with respect to bottom wall36. Access area 59 within a side wall defining combustion chamber 35,may provide easy access to each burner assembly 45, for installationand/or maintenance purposes.

[0062] While in the foregoing specification this invention has beendescribed in relation to certain preferred embodiments thereof, and manydetails have been set forth for purpose of illustration, it will beapparent to those skilled in the art that this invention is susceptibleto additional embodiments and that certain of the details described canbe varied considerably without departing from the basic principles ofthis invention.

What is claimed is:
 1. In a method for combusting a fuel and air mixturewithin a combustion chamber which in a pre-combustion condition containsan amount of fluid, wherein an exhaust flue forms communication betweenthe combustion chamber and an ambient environment, the improvementcomprising: discharging the fuel and air mixture from a flame holdingdevice; igniting the fuel and air mixture within the combustion chamber;and discharging a first portion of the amount of the fluid through apressure relief void in communication with the ambient environment anddischarging a second portion of the fluid through the exhaust flue. 2.In a method according to claim 1 wherein the first portion of the amountof fluid passes through the pressure relief void only upon ignition ofthe fuel and air mixture.
 3. In a method according to claim 1 furthercomprising controlling a rate of the fluid passing through the pressurerelief void.
 4. In a method according to claim 1 wherein the rate iscontrolled by sizing the pressure relief void to allow the first portionof the amount of fluid to pass through the pressure relief void uponignition and to prevent a combustion flame from passing through thepressure relief void during at least one of ignition and operationalcombustion.
 5. In a method according to claim 1 wherein the pressurerelief void is formed as a peripheral gap between a combustion chamberwall that defines the combustion chamber and the exhaust flue.
 6. In amethod according to claim 5 wherein the peripheral gap is in a rangefrom about 0.055 inch to about 0.065 inch.
 7. In a method according toclaim 1 wherein the fuel and air mixture is pre-mixed upstream of theflame holding device.
 8. In a method according to claim 7 wherein thefuel and air mixture is pre-mixed within a venturi.
 9. In a methodaccording to claim 1 wherein a first flow rate through the pressurerelief void is significantly less than a second flow rate through theexhaust flue.
 10. In a method according to claim 1 wherein thecombustion chamber is not substantially sealed.
 11. In an apparatus forcombusting a fuel and air mixture, the apparatus having a combustionchamber wall defining a combustion chamber, an exhaust flue formingcommunication between the combustion chamber and an ambient environment,the improvement comprising: a pressure relief void in communication withthe combustion chamber and the ambient environment, and the pressurerelief void sized large enough to relieve an ignition pressure from thecombustion chamber upon ignition of the fuel and air mixture and sizedsmall enough to prevent a combustion flame from passing through thepressure relief void during at least one of ignition and operationalcombustion of the fuel and air mixture.
 12. In the apparatus accordingto claim 11 wherein the pressure relief void is formed as a peripheralgap between the combustion chamber wall and a vessel wall of a vessel.13. In the apparatus according to claim 12 wherein the peripheral gap isin a range from about 0.055 inch to about 0.065 inch.
 14. In theapparatus according to claim 12 wherein at least one of the combustionchamber wall and the vessel wall has at least one spacer element thatfixes the combustion chamber wall at a distance from the vessel wall.15. In the apparatus according to claim 14 wherein the at least onespacer element comprises at least one of the combustion chamber wall andthe vessel wall having a protuberance positioned within the peripheralgap.
 16. In the apparatus according to claim 11 wherein a first area ofthe pressure relief void is sized according to a second area of theexhaust flue so that a first flow rate through the pressure relief voidis significantly less than a second flow rate through the exhaust flue.17. In the apparatus according to claim 11 further comprising a venturinozzle forming communication between the combustion chamber and a fuelsupply and an air supply.
 18. In the apparatus according to claim 11further comprising a plurality of burners mounted to discharge into thecombustion chamber.
 19. In the apparatus according to claim 18 whereineach of the burners has a self-supporting mat structure forming a burnersurface.
 20. In the apparatus according to claim 19 wherein theself-supporting mat structure comprises a plurality of ceramic fiberscoated with a silicon carbide material.
 21. In the apparatus accordingto claim 20 wherein the ceramic fibers are solidly welded together. 22.In the apparatus according to claim 11 wherein the apparatus is anatural draft and non-condensing gaseous fuel fired water heater.
 23. Amounting apparatus for releasably attaching a burner assembly to abottom wall that at least partially defines a combustion chamber of awater heater, the mounting apparatus comprising: a flange on the burnerassembly, a clip attached to the bottom wall, the clip having an endportion spaced from the bottom wall forming a receiver, a first portionof the flange engageable within the receiver, and a removable fastenerfastening a second end of the flange against the bottom wall.
 24. Themounting apparatus according to claim 23, wherein the clip comprises abase portion attached to the bottom wall and the end portion is offsetfrom the base portion.
 25. The mounting apparatus according to claim 23wherein the removable fastener comprises a screw having an end portionconnected to the bottom wall.
 26. The mounting apparatus according toclaim 23 wherein the removable fastener comprises a latch removablyengageable within a shoulder of the bottom wall.
 27. The mountingapparatus according to claim 23 wherein the clip has a slot and theburner assembly has a seam that engages within the slot to limitmovement in at least one direction of the burner assembly with respectto the bottom wall.
 28. The mounting apparatus according to claim 23wherein with the burner assembly mounted within the clip, the cliplimits movement in at least one direction of the burner assembly withrespect to the bottom wall.
 29. The mounting apparatus according toclaim 23 wherein the bottom wall accommodates two of the burnerassemblies.
 30. The mounting apparatus according to claim 29 wherein thebottom wall and the burner assemblies are mounted within a natural draftand non-condensing gaseous fuel fired water heater.
 31. In a gaseousfuel fired water heater apparatus having a bottom wall at leastpartially defining a combustion chamber, a fuel supply and an air supplyintroducing fuel and air into the combustion chamber, and an exhaustflue forming communication between the combustion chamber and an ambientenvironment, the improvement comprising: a plurality of burnerassemblies mounted to the bottom wall, the fuel supply and the airsupply in communication with each of the burner assemblies, and each ofthe burner assemblies having a burner exposed to the combustion chamber.32. In the gaseous fuel fired water heater apparatus according to claim31 wherein the burner assemblies are positioned a distance apart fromeach other forming a catch area between the burner assemblies.
 33. Inthe gaseous fuel fired water heater apparatus according to claim 32wherein the catch area is centrally located on the bottom wall forcatching at least one of debris fallout and condensation.
 34. In thegaseous fuel fired water heater apparatus according to claim 31 whereineach of the burner assemblies has a mounting apparatus for releasablyattaching the burner assembly to the bottom, and the mounting apparatuscomprises a flange on the burner assembly, a clip attached to the bottomwall, the clip having an end portion spaced from the bottom wall forminga receiver, a first portion of the flange engageable within thereceiver, and a removable fastener fastening a second end of the flangeagainst the bottom wall.
 35. In the gaseous fuel fired water heaterapparatus according to claim 31 wherein the gaseous fuel fired waterheater is a natural draft and non-condensing water heater.
 36. In agaseous fuel fired water heater apparatus having a bottom wall at leastpartially defining a combustion chamber, a fuel supply and an air supplyintroducing fuel and air into the combustion chamber, and an exhaustflue forming communication between the combustion chamber and an ambientenvironment, the improvement comprising: an arcuate burner assemblymounted to the bottom wall, the fuel supply and the air supply incommunication with the burner assembly, the burner assembly having aburner exposed to the combustion chamber, and the arcuate burnerassembly forming a centrally positioned catch area.
 37. In the gaseousfuel fired water heater apparatus according to claim 36 wherein thearcuate burner assembly is annular.